1. Field of the Invention
The subject invention relates to an antenna for receiving a circularly polarized radio frequency (RF) signal from a satellite.
2. Description of the Prior Art
Vehicles have long implemented glass to enclose a cabin of the vehicle while still allowing visibility for the driver of the vehicle. Automotive glass is typically either a tempered (or toughened) glass or a laminated glass which is produced by bonding two or more panes of glass together with an adhesive interlayer. The interlayer keeps the panes of glass together even when the glass is broken.
Recently, antennas have been integrated with the glass of the vehicle. This integration helps improve the aerodynamic performance of the vehicle as well to help provide the vehicle with an aesthetically-pleasing, streamlined appearance. Integration of antennas for receiving linearly polarized RF signals, such as those generated by AM/FM terrestrial broadcast stations, has been the principal focus of the industry. However, that focus is shifting to integrating antennas for receiving RF signals from Satellite Digital Audio Radio Service (SDARS) providers. SDARS providers use satellites to broadcast RF signals, particularly circularly polarized RF signals, back to Earth.
Various glass-integrated antennas for receiving RF signals are known in the art. Examples of such antennas are disclosed in the U.S. Pat. No. 5,355,144 (the '144 patent) to Walton et al. and U.S. Pat. No. 6,097,345 (the '345 patent) to Walton.
The '144 patent discloses an antenna integrated with a window of a vehicle. The vehicle includes a metal frame having an edge defining an aperture. The edge of the metal frame is electrically conductive and supports the window. The window includes two panes of glass sandwiching an adhesive interlayer. An electrically conductive film is bonded to a surface of one of the panes of glass and defines a slot between the film and the edge. A conductive layer is disposed on another of the surfaces of the panes of glass. A center conductor of an unbalanced transmission line is connected to the conductive layer and a shield of the unbalanced transmission line is connected to the metal frame. The conductive layer acts as a feed line to electromagnetically couple center conductor to the electrically conductive film. The antenna of the '144 patent is not configured to allow reception of circularly polarized RF signals. Furthermore, the antenna of the '144 patent contains no provisions for matching an impedance of the antenna to an impedance of the unbalanced transmission line.
The '345 patent discloses an antenna integrated with a window of a vehicle. The window is supported by a metal frame of the vehicle. The window includes two panes of glass sandwiching an adhesive interlayer. In one embodiment, a conductive layer is disposed on one of the surfaces of the panes of glass. The conductive layer defines a slot having two slot legs with resonance on two frequency bands. A feed line is disposed on another of the surfaces of the panes of glass. A center conductor of an unbalanced transmission line is electrically connected to the feed line. The feed line then acts as a capacitive coupling to the conductive layer. A shield of the unbalanced transmission line is electrically connected to the metal frame. The antenna of the '345 patent is not configured to allow reception of circularly polarized RF signals. Furthermore, the antenna of the '345 patent contains no provisions for matching an impedance of the antenna to an impedance of the unbalanced transmission line.